Solar panels are much more efficient with cool water entering, lower cost un-glazed panels are a perfect match for recharging ground loops.
See graph below
Preliminary Review of Geothermal Solar Assisted Heat Pumps - Appropedia: The sustainability wiki
"Geothermal heat pump systems are commercially available in a variety of arrangements to be used in the heating and cooling applications of buildings. A major drawback of such systems is the long term operational consequence of decreasing ground temperatures, resulting in lower system performance. In recent developments so called “hybrid-systems” have been examined to address this issue. In these systems an independent energy source, potentially solar, is used to accommodate the unbalanced annual loads that often exist under certain climatic or load conditions "
http://www.ibpsa.org/proceedings/BS2011/P_1941.pdf
" In heating only or heating-*dominated applications,
the yearly load imbalance leads to ground cooling
over the years. The borehole length must be
increased to cope with that fact, especially in larger
systems with multiple boreholes that thermally
interact with each other. Supplemental heat sources
such as solar collectors have the potential to reduce
the required length of ground heat exchanger, hence
the capital cost. "
https://intraweb.stockton.edu/eyos/e...cations/83.pdf
" The benefit of using solar heat in the system with ground-source heat pump depends on the performance of the actual system. If the bore holes are too short for the system and heat demand, the best savings of electricity is to use the solar heat during summer time for domestic hot water and during winter timefor recharging the borehole.
The benefit of recharging during summertime is very limited. "
http://www.geothermal-energy.org/pdf...13/Maritan.pdf
" In the near future, for ground source heat pumps,
compact ground heat exchangers should probably be
an answer for small gardens, without expensive
borehole drillings. Solar re-charging of ground loops
is today a field of research in the geothermal heat
pumps industry. This article illustrates the case of a
residential 6kW geothermal heat pump system
installed end of 2011 in the north of Italy, with a soil-water heat pump and
compact ground collectors with solar re-charge. Data from the system monitoring are
here presented and discussed. "